Texas law famously exempts septic systems on tracts over 10 acres from permitting requirements. Not in Grayson County. The county’s OSSF order requires a permit, authorization to construct, and inspection for every residential or commercial system (new, altered, extended, or repaired) “regardless of the size of the tract of land.” That’s the opening move in the most prescriptive septic order among the counties we’ve profiled, and anyone shopping land between Sherman, Denison, and the Lake Texoma shore should read it before closing.
The order’s centerpiece: any lot under 2.5 acres must use aerobic treatment. No conventional system, period. Minimum lot sizes stack on top: 1.5 acres per structure without public water (1 acre if every system is subsurface drip), 1 acre with public water (half-acre all-drip). A public sewer within 100 feet? You connect, absent County Engineer sign-off. Even self-maintenance is gated: owners may service their own aerobic units only after passing a county-approved course and signing an agreement, and they forfeit the privilege by failing to submit reports. RV parks get their own regime: four or more RVs means aerobic treatment with no surface spray at all, a trash tank per five spaces, a density capped at about seven RVs per acre, and a design flow of at least 80 gallons per day per space. Little of this is guesswork for the county’s engineers: it’s written down, and we cite it directly.
Why so strict? Look at the map. The county’s north drains straight into Lake Texoma and the Red River through acidic Post Oak sands and loams; the south runs Blackland clay toward Trinity River tributaries. Sandy soils move water (and poorly treated effluent) quickly toward a lake ringed with septic-dependent communities such as Pottsboro, Preston, and Sherwood Shores. The permit ledger shows the order at work: 774 systems authorized in 2024 (15th statewide, on a county of 136,000), 632 of them (82 percent) aerobic surface-irrigation units, exactly what the 2.5-acre rule predicts. The decade total: 6,366.
If that sounds like a county where the permit guide earns its keep, it is. Owners should also understand aerobic contract duties, since the county actively polices reporting, and keep pump-out schedules documented for resale.
Grayson County office: 100 W. Houston St., Suite G-3, Sherman, (903) 813-4247, M–F 8–12 and 1–5. Permit walkthrough here.
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New installs and major repairs need a permit from the local authorized agent — usually the county, sometimes a city — and the rules that bind are the local ones.
Our permit guide covers fees, required professionals and every step.
Four things decide what you can build and what it costs: zoning, environmental protections, power for aerobic systems, and the ground itself. We publish each one only where we have checked it — and say so plainly where the answer is “same as the rest of Texas”.
Zoning & land use
Grayson County issues the septic permit for the whole county. It holds that job only because the commissioners court adopted an on-site sewage facility order and TCEQ approved it (Health and Safety Code § 366.031), and § 366.032(b) makes that order prevail wherever it is stricter than 30 TAC Chapter 285. Ask the office for its current order — Texas counties have no general zoning power, so the order, not zoning, is where a local siting rule sits.
Nothing in Grayson County changes this.
Texas adds a separate approval path over the Edwards Aquifer recharge, transition and contributing zones, where TCEQ requires an Edwards Aquifer Protection Plan under 30 TAC Chapter 213. Elsewhere the Chapter 285 rules stand on their own.
The dominant constraint here is clayey subsoil that water moves through too slowly (69.9% of rated soils), followed by bedrock close to the surface (27.3%). NRCS rates 80.2% of rated ground very limited for a standard soil absorption field, 21.9% for subsurface drip and 12.1% for surface application with disinfection. Where a conventional field will not pass, surface application is usually the route that does.
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